Method of producing copperplated culinary vessels



March 29, 1949. A. c. scAvuL-Lo METHOD OF PRODUCING COPPERPLATED CULINARY VESSELS Original Filed April 17, 1944 p I Imus/v70? JzgeZo agcaz/ulio 1716' x97- ro FIVE) Patented Mar. 29, 1949 UNITED STATES PATENT OFFICE METHOD OF PRODUCING COPPERPLATED CULINARY VESSELS Original application April 17, 1944, Serial No. 531,441, which is a division of Serial No. 329,188,

April 11, 1940.

Divided and this application 7 August 13, 1945, Serial No. 610,415

3 Claims. I

This application is a division of my copending application, Serial No. 531,441, of April 17, 1944, entitled Cooking utensils and method, which in turn is a division of my U. S. Letters Patent 2,358,104, entitled Cooking utensils and method, of September 12, 1944, the application Serial No. 329,188 for which was filed April 11, 1940, which in turn is a continuation-in-part of application 154,246, filed July 17, 1937, entitled Cooking utensil, now abandoned, and the invention relates to the production of cooking utensils having desirable heat conduction and corrosion resistance characteristics.

Among the objects of my invention is to provide a simple, direct, efficient and economical method and apparatus for making a rugged and durable utensil which is highly resistant to the corrosive attack of foods and also has high lateral heat conductivity so that food placed therein may be heated uniformly without requiring constant attention and without the food being scorched by local hot spots.

Other objects will in part be apparent and in part pointed out hereinafter.

The invention accordingly consists in the combination of elements, features of construction and arrangement of parts, and in the several steps and the relation of each of the same to one or more of the others as described herein, the scope of the application of which is indicated in the appended claims.

In the accompanying drawings,

Figure 1 is a diagrammatic representation of the apparatus employed to carry out one step of forming my utensil.

Figure 2 shows the method of attaching a handle to the utensil, and

Figure 3 is a cross-sectional view of the completed utensil with the handle attached.

Like reference characters refer to like parts throughout the several views of the drawings.

As conducive to a clearer understanding of cer tain features of my invention it may be noted at this point that it is desirable to use stainless steel as a material for the construction of cocking utensils because of its superior resistance to the corrosive attack of foods. A serious objection to its use is that it has low heat conductivity. Heat applied to one portion of a pan made solely of stainless steel does not diffuse to the other portions of the pan but remains concentrated in the one portion with the consequence that food on that portion will be burned and food in other portions will not be cooked unless the mass of food is continually stirred.

2 It has been proposed to make a utensil of stainless steel on the inside and thick copper on the outside as copper possesses excellent heat conductive characteristics. A number of utensils of this character were made by having the twometals tightly fitted together and spot-welded but this previously was not successful due to the danger of a crack forming between the metals and water going into the crack. In one case this crack became partially closed so that, on heating, the steam generated caused a rupture of the vessel. Efforts have been made to electrodeposit or spray copper on stainless steel but without success because the copper tends to peel oil and form blisters.

In the prior art, it has been proposed to apply a layer of conductive material to the bottom or a stainless steel vessel by riveting, casting, or other method. A vessel so formed is not satisfactory because heat is not readily conducted to its sides as well as its bottom and consequently the heating of food therein will still be uneven. Furthermore, such a vessel has been found in practice to be defective because of tendencies to become warped and blistered in use. It has also been proposed to construct a vessel with an inner layer of stainless steel, an intermediate layer of mild steel or cuprous alloy and an outer layer of enamel. Such a vessel is obviously ineflicient because of the low heat conductivity of enamel, which has the further disadvantage that it becomes chipped when subjected to heavy handling.

According to this invention copper has been successfully united to the sides as well as to the bottom of a stainless steel vessel without any danger of having the copper tend to peel off. Specifically this is accomplished by the interposition of a layer of ordinary steel to which the copper is adapted to adhere better than it does to the stainless steel.

In the past, handles have been secured to cool:- ing vessels by riveting them on. That method of attaching a handle has the disadvantages that it involves several steps and the handle is liable to work loose in heavy use. In my invention, I provide for welding the handle to the vessel so that a firm union of pleasing appearance is formed in an operation which is simple and inexpensive.

Referring now more particularly to the practice of my invention, attention is directed to Figure 1 of the drawing wherein, illustratively, I have shown a suitable form of my apparatus for applying a copper coating to the vessel by an electroplating process.

The inside portion of the vessel is formed of a of being intimately united withthe copper. .For.

this purpose ordinary non-stainless or mildsteel is used. The thickness of the mild steel layer ll may be less, about the same, or greater than the thickness of the stainless steel liner [0, though preferably due to its thermal function in this invention it is made thicker than the stainless steel liner, The layers Ill and H are intimately united at the mill by heat and rolling and the duplex steel purchased from the mill in sizes and thicknesses desired. After being cut to size the sheet material is shaped between forming dies in order to provide a cooking utensil of the desired kind. In the shaping, of course, care must be taken to see that the stainless steel liner is on the inside because the non-stainless steel is adapted to have copper united thereto in a more satisfactory fashion than the copper is capable of uniting to the stainless steel. In this way, the thick copper layer may be indirectly attached to the stainless steel since the liner H is intimately united with the stainless steel at the mill.

The outside of the vessel is cleaned by pickling or in other ways and its inner stainless steel surface is coated with beeswax to prevent the depositing of any copper thereon. The vessel is put into position for electroplating in the tank l2. A copper bar I3 is soldered to the inside of the vessel as at M and I5 to establish good electrical contact, the bar in turn being mechanically and electrically connected at IE to a copper shaft l1, which is adapted to be rotated by some suitable means not indicated in the drawing. The shaft I1 is rotated at a speed which will give a linear velocity of approximately 6 feet per minute to the periphery of the vessel for a purpose which is hereinafter referred to, the speed of rotation in revolutions per minute of course depending upon the diameter of the vessel being plated.

The shaft I 1 is electrically connected by way of a copper spring contact brush l8 and a lead l9 to the negative terminal of a source of direct current electrical energy such as a storage cell 20. The positive terminal of the source 20 is connected by lead 2! to a metallic rod 22 which is secured in a position near the inside top edge of the tank [2 but insulated from the tank. Copper plates or bars 23are suspended from the rod 22 on metallic hooks 24, which provide an elec'- trical connection between the rod 22, the plates 23, the latter forming the anodes of an electro-,

lytic cell. A suitable electrolyte 25 is contained in the tank l2 at a level high enough to completely submerge the vessel being plated. This electrolyteis preferably a copper sulphate solution containing a small amount of sulphuric acid but other solutions may be used. By virtue of its connection to the negative terminal of the source 20, the vessel forms the cathode of the electrolytic cell.

In the plating operation, after all the connec tions are made, the vessel is rotated at desired speed by the shaft I'l. Due to electrolytic action, the copper of the anodes 23 is dissolved in the electrolyte 2-5 and copper from the electrolyte is in turn deposited on the outer surface of the mild 4 steel layer ll. As indicated above, none is deposited on the stainless steel inner layer because that layer is protected by a coating of beeswax. The deposited copper fills interstices and covers surface irregularities in thelayer ll. The electroplating operation is continued until it builds up a layer of copper 26 as shown in Figure 3 of .suffi'cient thickness that the copper forms a path "of high conductivity.

The method of electroplating described herein is ,characterizedby extreme simplicity in the apparatus required and in operation. The copper coating deposited on the vessel is of uniform thickness except on the bottom edge, where it is desirably somewhat thicker than on other portionsof the vessel. Due to stirring of the electrolyte caused by rotation of the vessel no gas bubbles are included in the copper coating which is accordingly solid and dense.

Due to the time and current requirements for electro-depositing the large. bulk of copper itmay be preferred tobuild up the layer 26 to the desired thickness by the spraying of hot copper particlesafter a'firs-t .coat of electro-deposited copperhas beenapplied. The copperis a much better conductor of heat than either theliner Ml. or the layer ll and thereforeit assists in evenly distributing heat around the cooking vessel in use was tov preventas .far aspossible theformation of local hot spots which might cause burning. or scorching of the "food whether inliquid or solid form.

In coating the vessel, a coat of copper of thicker cross section than thatof the. rest of the copper This thickened .portion is illustrated at 21in Figure 3. It serves the function of thermally reinforcing the junction between the bottom and side walls. is provided between the bottom of the utensil to which the heat is usually applied and the-side Walls.

After the vessel has had its copper wall built up to the desired thickness, preferably such that the copper and mild steel layers combined are substantially thicker than the stainless steel liner, the outer surface is trimmed and smoothed or finished in any well known manner. The vessel is then ready to have its handle attached.

Referring now to Figure 2 it will be seen that the handle 28 has an enlarged lower end .29 which is placed in contact with the side of the vessel and welded thereto. The handle is preferably an alloy containing about 58% copper, 20% zinc, 1% lead and 1% aluminum. Such an alloy has a melting point of about 1800? F. which is slightly below the melting point ofv the coppercoating 26 on the outside of the vessel; copperhas a melting pointof about 1982" F.

In order to attach the handle its enlarged ,end

29 is heated to a welding heat andthen placed contiguous the copper coating of the utensil when it may; be held in place by means of the clamps 30 until welded. .In order to prevent bending the walls of the vessel from their desired shape. an iron or steel block 3| is madeof a size to As as result, better heat conduction in the present instance because the steel layers are functionally useful not only in mechanically reinforcing the copper during the welding so as to prevent plastic flow of the copper under the pressures used in the welding process, but also in reducing dissipation of heat from the welding area due to the relatively poor heat conductivity of steel. The dotted lines 32 indicate the location of the bluish discoloration in the stainless steel liner after welding which shows that at least the stainless steel does not have time to be heated to any extent sufficient to produce .such a discoloration for more than about 20 to 30 degrees away from the ends of the welded handle portion 29.

It is to be understood that the invention contemplates a cooking utensil of any desired shape, the form shown merely exemplifying one of a number of possible and desirable shapes.

The cooking vessel of my invention is characterized by excellent heat conductivity of bottom and side walls. As a. consequence, heat applied to the bottom will be distributed over the whole of the bottom and side walls and food within the vessel will be heated uniformly. The increased thickness of copper at the junction between the bottom and sides of the vessel has been found desirable in better distributing the heat up the side walls from the bottom. In other words, it has been discovered that increased and satisfactory heat transfer can be made possible by thickening the copper coating only at the junction between the walls and bottom and without the necessity of having the bottom and side walls of a greater thickness. The thickened edge portion is also desirable because a substantial thickness of copper remains on the edge even after the vessel has been subjected to wear caused by the rough handling encountered in actual practical use.

The particular reason why deposited copper adheres mor firmly to the ordinary steel layer H than it does to the stainless steel layer I is not known nor understood. Moreover, the reason why my vessel is free from warping also is not understood because the stainless steel layer ID has a coeflicient of expansion closer to that of copper than does the layer II. It was this closeness in coefliciency of expansion that may have misled the prior investigators and caused them to exert their efforts toward uniting copper and stainless steel directly. At any rate, these efforts at directly uniting copper and stainless steel have not proven satisfactory and the discovery of this invention appeared at first to be a step in the wrong direction.

However, cooking vessels made under this in vention have been tested out for some time and found to be commercially satisfactory. Due to the intimate uniting between the three layers [0, H and 12, no protecting bead of stainless steel is necessary to be formed.

A particular advantage of my vessel is its freedom from the warping and blistering which are encountered in vessels of two-ply material after a certain amount of use. The freedom from warping may be due to the fact that the metals having approximately equal coefficients of expansion, namely the stainless steel inner layer and the copper outer layer, counter-balance each other, the relatively thick inner layer of mild steel serving as a stiffener. Whatever may be the true explanation of this property, it forms an important feature of my invention. The other property mentioned, namely freedom from 6 blistering is also very valuable. characteristic to the particular process of electroplating employed. Rotation of the vessel during this process insures an even deposit of copper because the rotation causes removal of gas bubbles from the vessel .surface. Thus, as the copper layer is formed, no gas is trapped between the copper and the base metal.

Among the advantages of this invention may be mentioned the much improved and neater utensil, the handle of which is united by welding and therefore eliminates the necessity for riveting as has heretofore been customary. A particular advantage of this method of attaching the handle is that no warping of the vessel is caused by it. Such warping would almost inevitably result were the whole vessel to be heated.

Thus, it will be seen that there is had in my invention a utensil and method of producing the same in which the various objects hereinbefore set forth, together with my thoroughly practical advantages, are successfully achieved. It will be seen that the vessel is rugged, and well adapted to handling in use, that it is calculated to be free of warping and blistering in use, and that it is designed to give uniform heating through bottom and side walls. Also, it will be seen that my utensil is produced in a simple, direct, and efilcient manner.

As many possible embodiments may be made of my invention and as many changes may be made in the embodiments hereinbefore set forth, it will be understood that all matter described herein, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In the production of a culinary vessel having bottom and side wall portions with an inner stainless steel surface and a copper outer surface, the art which includes supporting a partially formed vessel comprising a layer of mild steel and an inner surface layer of stainless steel for vertical axial rotation by means also providing electrical contact to the stainless steel surface by way of soldered joints, immersing the partially formed vessel in a copper plating bath, passing electro-plating current through said vessel by way of said soldered joints, and rotating the partially formed vessel by way of said supporting and contact soldered points while passing said electroplating current and electrodepositing copper onto the exterior surface thereof to achieve said copper outer surface without electrodepositing on said inner stainless steel surface.

2. In the production of a culinary vessel comprising bottom and side wall portions with inner surface of stainless steel and outer surface of copper, the art which comprises pickling the exposed surface of a partially formed vessel comp ng a layer of mild steel and an inner surface layer of stainless steel, waxing the inner stainless steel surface layer, supporting said partially formed vessel for vertical axial rotation by means also providing electrical contact to the stainless steel surface by way of soldered joints, immersing the partially formed vessel in a copper plating bath, passing electrical current through said vessel by way of said soldered joints, and rotating the partially formed vessel by way of said soldered joints while passing said electroplating current therethrough and electrodepositingcopper onto the exterior surface thereof to achieve said outer surface of copper while precluding I attribute this 2,4653608: electrodeposition on: saidlinner stainless steel sur-, copper while precluding electrodepositionzon said face. inner stainless steel surface.

3. In the production of. a culinary vessel com- ANGELO C. SCAVULLO. prising bottom and side wall portions with inner surface of stainless steel and outer surface of 5 REFERENCES CITED copper the art which comprises covering the? The following references are of record in the inner surface layer of a partially formed vessel me of this patent: consisting of an outer layer of mild steel and an inner layer of stainless steel with a protective UNITED STATES PATENTS material for preventing electrodeposition on such 10 Number Name R Date surface, supporting said partially formed vessel 193,204 Wilde July 17 1377' for vertical axial rotation, by means also provid- I 415,024, Comn 12, 1839v ing electrical contact to the Stainless steel surface 536,171 Fletcher July 13, 1397 by way of soldered joints, in a copperplating 51 7 Richards Nov. 11, 1924 bath containing a small amount of sulphuric acid, 15 2,363,973 Kennedy et 23, 1944 and passing electrical current through said vessel 1 by way of said soldered joints, while rotating the OTHER REFERENCES partially formed vessel by way of said soldered Principles of Electroplating and Electroformjoints, and electrodepositing copper onto the mild ing, by William Blumand George B. Hogaboom, l steel surface to achieve said outer surface of 2d edition, 1930, pages 180, 198, 199. 

